Podoplanin is a highly sensitive and specific marker to distinguish primary skin adnexal carcinomas from adenocarcinomas metastatic to skin.

Distinction of primary skin adnexal carcinomas from cutaneous metastasis of adenocarcinomas is challenging. In this study, we evaluated podoplanin immunoreactivity in a series of primary skin adnexal tumors and adenocarcinomas metastatic to skin using a D2-40 antibody. The initial test series were composed of a total of 93 cases including 32 primary skin adnexal carcinomas, 46 benign primary adnexal tumors, and 15 cutaneous metastatic adenocarcinomas. We found that variable D2-40 reactivity was seen in all of the primary cutaneous carcinomas including sebaceous carcinomas (10/10), squamous cell carcinomas (10/10), porocarcinomas (4/4), trichilemmal carcinomas (4/4), skin adnexal carcinomas not otherwise specified (4/4), and in the majority of benign skin adnexal tumors. In contrast, no podoplanin immunoreactivity was seen in any of the 15 (0/15) cutaneous metastases. To confirm the initial findings and to further explore the utility of podoplanin reactivity in the distinction of these tumors, we also examined a test set of 35 unknown cases, including 21 adenocarcinomas metastatic to skin and 14 primary adnexal tumors, in a blinded fashion. In this test set of cases, podoplanin was negative in 22 cases and positive in 13 cases. Of the 22 podoplanin negative cases, 20 were proven to be metastatic adenocarcinoma. Of the 13 D2-40 positive cases, 12 were proven to be primary adnexal tumors. Our results suggest that podoplanin can be a useful tool to distinguish primary skin adnexal carcinomas form adenocarcinomas metastatic to skin with high sensitivity (94.5%) and specificity (97.2%).